Cementitions flooring compositions are well known and widely used where smooth and chemically and mechanically resistant flooring solutions are required. In many such applications, epoxy resin based flooring compositions offer a suitable solution, also due to the fact that they often provide aesthetically pleasing and glossy surfaces. On the other hand, epoxy resin based flooring compositions suffer from certain disadvantages. For example, undesired blushing effects may occur, especially at lower temperatures. Also gloss intensity is often influenced by temperature and may decrease on cold environments. Furthermore, the chemicals involved (i.e. epoxides and amines) are increasingly considered hazardous by European Union Regulation REACH, so that an alternative chemistry to overcome such limitations is desirable.
Polyurethane (PU) cementitious hybrid systems are known to offer an alternative solution for the preparation of coating and flooring products that have outstanding mechanical properties and do not suffer from the drawbacks associated with epoxy resin compositions. However, such PU hybrid systems generally exhibit dull or matt surfaces, which is an unfavorable restriction with respect to aesthetic demands, as the visual aspect of the surface of a coating or flooring is an important feature. Furthermore, dull or matt surfaces are sometimes difficult to clean, for gloss is often associated with surface smoothness.
Polyurethane cementitious hybrid systems are complex systems wherein during curing of the precursor components two main reactions occur, namely the reaction of a polyol and a polyisocyanate to form the polyurethane and the reaction of cement and water, generally called hydration. Upon hydration the cement is hardened to a solid material. The hydration is usually effected in the presence of aggregates such as sand or gravel so that the aggregate particles are bound together by the cement material to obtain mortar or concrete.
Since both reactions take place in the same mixture, it is almost unavoidable that unwanted side reactions occur. Specifically, the reactive isocyanate compounds can react with water resulting in the generation of amine compounds and CO2 gas. The generation of CO2 is a problem since it may lead to blister formation. Moreover, the formation of amines prompts a consecutive side reaction since the isocyanate compounds also react with amines to form urea compounds.
Due to the complex reactions and side reactions, it is difficult to modify the systems without affecting mechanical and workability characteristics and open time. In order to diminish unwanted side reactions and to maintain a sufficiently long shelf life, such PU cementitious hybrid systems use a three component composition, including basically a water/polyol component, a hardener (polyisocyanate) component, and a cement component. With such a three component setup it is possible to create stable compositions which yield smooth, mechanically and chemically resistant flooring surfaces after mixing and application. However, as mentioned before, they generally produce rather dull or matt surfaces which do not exhibit the appealing gloss of epoxy resin based compositions and are often difficult to clean.